Electrostatic liquid cleaners



Dw- 15, 1959 E. sAuER Re. 24,751

ELECTROSTATIC LIQUID CLEANERS Original Filed Dec. 28. 1956 miredl States Patent' 0P ELECTRGSTATIC LIQUID CLEANERS Louis E. Sauer, Sharon, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corpora- `tion of Pennsylvania Original No. 2,876,193, dated March 3, 1959, Serial No. 631,293, December 28, 1956. Application for reissue May 4, 1959, Serial No. 810,981

(Cl. 20k-305) 3 Claims.

This invention relates to electrostatic liquid cleaners, and has as objects to simplify and reduce the cost of such. cleaners. v

This invention provides a simple, inexpensive, troublefree, electrostatic precipitator which has been found to be particularly suitable for removing the carbon formed by arcing in insulating oils oftap changing compartments of transformers.

In one embodiment of this invention, a series of spacedapart metal plates inserted within a [conductive] liquid to be cleaned, forms a voltage divider to ground [in the same manner that the spaced-apart plates of well known liquid rheostats do]. Alternating current from a line or from a bushing potential tap is applied across the plates. A central plate is connected to ground through a halfwave rectifier which has a maximum-inverse voltage equal to one-half the voltage across the plates. During alternate half-cycles, the rectier conducts and shorts out half of the plates, leaving the applied voltage across the other half of the plates. During the `other half-cycles, the applied voltage is acrossv all of the plates. This results in a net acceleration D.C. voltage of one-half the applied voltage, which D.C. voltage is suicient to provide adequate electrostatic elds between adjacent plates for collection of foreign matter in the liquid.

This invention will now be described with reference to the annexed drawings,tof which:

Fig. l is an end section of an electrostatic liquid cleaner embodying this invention; 1

Fig. 2 is a side section of the cleaner;

Fig. 3 is a side elevation of one form of collector plate; Fig. 4 is a side elevation of another form of collector plate; t Y Fig. 5 is a circuit schematic showing how the collector plates are energized, and

Fig. 6 is a graph showing the Wave forms of the voltage at the collector plates of the cleaner.

A metal casing 9 has a vertically extending side 10 and has an opposite side with a lower portion 11 which slants inwardly towards the bottom of the casinl and has vertically extending ends 12.

Plates 13 of electric insulation are attached to metal brackets 14 which are attached to the inner surface of the casing side 10. The plates 13 have circular holes 15 and 16 extending therethrough to receive rods 17 and 18 respectively, which extend outwardly from the ends of similar collector plates P1 and P3. The plates 13 have circular holes 20 and 21 extending therethrough to receive rods 22 and 23 respectively, which extend outwardly from similar collector plates P2 and P4. The plates 13 thus support the plates P1-P4, insulated from each other. The rod receiving holes in the plates are so arranged that the collector plates P1-P4 converge towards the bottom 27 of the casing. Placing E,the sup- Re. 24,751 Reissues nec. 15, 1,959

nce

porting rods on adjacent plates out of horizontal alignment increases their insulating spacings.

The collector plates P1-P4 are spaced apart in the order given, the plate P1 being one of the outermost plates. The plate P1 is spaced suliiciently from the adjacent side 11 of the casing for adequate insulation. The other outermost collector plate is plate P5 which is attached, as by spot welding, to the brackets 14, and extends through slots 26 in the plates 13, the brackets 14 and the slots 26 being so arranged that the plate P5 converges towards the adjacent plate.P4. Therplate P5 is longer than the other collector plates, so that its lower end is adjacent to the bottom 2.7 of the casing. The central plate P3 extends vertically. The plates P1-P5 have parallel, longitudinal axes. The plate P5 and the opposite side 11 of the casing converge towards the bottom of the casing for causing collected matter to be directed into drain passages 28 located in the bottom 27 of the casing between the lower ends of the collector plate P5 and the casing side 11. The passage 28 would have a valve connected thereto which is not shown.

The slots 26 in the plates 13, through which the collector plate P5 extends are wider in the lower portions of the plates 13 than they are in the upper portions of the plates 13 for decreasing the dielectric stress on the lower portions of the plates 13 so as to prevent conducting paths from being formed across the lower portions of the plates 13 where the plate P5 more closely approaches the adjacent collector plate P4.

The casing has a removable top 30 for providing access to the collector plates.

As shown by Fig. 5, the collector plate P5 is connected to power line L1. The collector plate P1 is connected through a resistor 31 to power line L2. The central collector plate P3 is connected through half-wave rectier 32 to L1. The collector plate P5 since contacting thev metal bracket 14 connected to the metal casing 9, is connected to and grounded to the casing.

The casing 9 contains a [conductive] liquid 35 to be cleaned, such, for example, as transformer oil containing carbon or other conductive or charged particles to be removed [the liquid 35 acting as a resistor providing a voltage drop of E/ 4 between each pair of adjacent plates P1P2, P2-P3, P3-P4 and P4--P5]. The plaies P1-P5 act as a capacitor voltage divider, each intermediate plate taking 0n a charge by electrostatic induction, the voltage of which depends upon the position .of such intermediate p late in the electrostatic field between outer plates. The plates P2 and P4 provide a large por tion of the required collection surface, and also reduce the voltage between adjacent plates to one-half that which would be required if they were not used.

The rectifier 32 since connected to a center and an end plate needs to have but one-half the voltage rating of a rectilier connected in series with all plates. Another advantage of connecting the rectier to a center plate is that charged particles to be collected migrate both ways from the center plate as will be brought out in the description of operation to follow.

In operation, the rectifier 32 would conduct during alternate half-cycles, and short out the plates P3-P5. A D.C. voltage of E would appear across the plates P1--P3, and there would be zero voltage across plates P3P5 during such alternate half-cycles. The positive half- Waves of Fig. 6 are the E voltages across plates P1-P3 during such alternate half-cycles. During the other halfcycles, there would be E voltage across all of the plates with E/2 voltage across the plates P1P3 and across the plates P3-P5. The negative half-waves of Fig. 6 are the E/Z voltages across P1-P3 and P3-P5 during such other half-cycles. Thus, there is a net particle accelerating voltage of E/2(EE/2) which is positive,

24,751Y v i across the plates Pil-P3 during all half-cycles, and a net accelerating voltage ofv E/2(E/2-0) across the plateS Pi-P during all half-cycles, the latter voltage of E/2 being negative. r

The foreign particles in the voil` are, given el'ectio static charges by electrostatic induction, ther polarities and values of which depend upon their positions in the electrostatic vlields between adjacent plates, areattracted tothe plates having opposite polarities, and are` repelled by the plates havingthe same polarites. Referringnow to Fig. 5, during all half-cycles, the netplus E/ZVoltage across the plates P1-lE34 causes charged particles between such plates to migrate from P3 towards P2, and from .P2 towards P1, collecting` upon the adjacent, ,downwardly slopingY surfaces of.' P`2` and P1,` and the net negative voltage of E/24 across-the plates P3L-P5' causesv charged particles between such, plates to migrate from P3 to-v wards P4, and from P4 `towards P5', collecting upon theadjacent, downwardly sloped surfaces of PlandA P5; The surfaces ofthe plates upon`which the particles deposit are the upper surfaces ofthe sloped' plates, and gravity aids in causing the particles to adhere to the plates as they drain down their surfaces. lf the particles were collected on the under surfaces of the plates P2 and P4, those surfaces facing plates P14 and P5"'respec tively, gravity would tend to cause such particlesto fall` off the plates.

The collector plates Plv-P5 converge towardsv eachA other lfrom their tops to their bottoms not only to facilitate adherence to the plates as described in theforegoing, but to increase the dielectric stress between the lower plate portions for collecting the smaller foreign particles which might escape collection by the more widely spaced, upper plate portions. This also aids in causing the liquid to recirculate from the bottoms of the plates over their tops.

The alternating current applied between the plate P1' and the adjacent, widely spaced wall 11 ofthe .casing has no adverse effect upon the migrationof particles between adjacent plates P1--P5, andresults in no collection upon the casing walls since thef alternating current could only. cause the particles to surge back and forth in the passage provided for spacing and recirculation, between the plate P1 and the wall 11. The surgingof the'particlesback and forth under the'inuence ofthe alternating,y current would heat the liquid and aid in its recirculationvfrom.

the bottoms of the plates over their tops.

The collected` particles agglomerato on the top surfaces of the plates P1, P2, P4 and P5, and slide down the plates falling off their bottoms in the form of sludge.

I claim:

1. An electrostatic liquid cleaner comprising, a casing for receiw'ng and containing a [conductive] liquidtobe cleaned,` a vertically extending, t, central collector. plate in said casing, an equal number of spaced-apart, collector plates with Substantiallyparallel, longitudinally extending axes, in said casing on each side of said central plate and sloped towards the bottom of said central plate so as to form passages between adjacent plates which converge towards said bottomtof saidcentral plate, [said plates beingg. arrangedrtorhaver theirlower: portions immersed in said liquid,] means for insulatedly supporting saidv plates whereby each platewis electrically insulated [exceptfor'said liquidfrfrom` the other plates, a halfwave rectifier having a terminal of one polarityy connected to said central plate, and having a terminal ofthe opposite polarity connectedto` amend onetof said. plates,

and means for supplyingwaltemating:'current.to.the: end

ones of said plates. v

2. An electrostatic liquid cleaner as claimed in claim l in whichsaid casing isrnetal, `in which oneend` of onefof saidy plates'is grounded tofrsaid' casing and extends toadjacentl the bottom of said-casing be1ow=the-lowerendsof the others of said plates, and in which saidcasing' has a wall opposite and spaced from the other end one of'said plates, said wall' havingav lower wallportionthat slopesl to said casing' bottomstowards'th'e'bottom of'said one end plate, said one end plate and said wall 'portion forming therebetween arpassagey below'saidothers Vof said plates that `converges towardsdsaidcasingbottom.

3. An `electrostatic liquid cleanercomprisinga casingl for receiving and containinga [conductive] liquid' to'be" cleaned, an odd number of generally vertically` disposed' spaced-apartU collector-plates extending in" a` row'in said casing` withA their longitudinall axes" parallel, [and: ara` ranged to have their lowerYV portionsV immersed" in said liquid] means for supporting said plates so" that each" is electrically insulated [except-for said' liquid] from' the others,` a half-wave rectifier having aterminal ofone4 polarity connected tothe centralI one" ofsaid plates, and having'a\terminal of the 'opposite polarity connected to an end-one of said plates, andl means for'supplyingal` ternating-currentn to the endv onesof saidf plates.

ReferencesCited in the file of this patent orfthe original patent UNITED STATES PATENTS" France Oct. 28, 1973.8; 

